The present invention relates to a process for producing a high concentration phosphoric acid and a gypsum by-product from phosphate rock. Uranium is normally present in the phosphate rock. The present invention resides in rendering the uranium readily recoverable in said process.
More specifically, the present process produces a high concentration phosphoric acid and a gypsum by-product by the steps of digesting phosphate rock and sulfuric acid to form a slurry containing the high concentration phosphoric acid and calcium sulfate hemihydrate crystals, filtering to separate the phosphoric acid, reslurrying the hemihydrate to produce calcium sulfate dihydrate and a low concentration phosphoric acid, and separating the dihydrate as a by-product and recycling the low concentration phosphoric acid, all as described in U.S. Pat. No. 3,653,826.
More commercial facilities use a wet process for producing phosphoric acid at a low concentration of about 30% P.sub.2 O.sub.5. This acid is normally evaporated to higher concentrations for practical applications, which naturally involves additional expense and process steps using large quantities of steam.
Phosphate rock normally contains small amounts of uranium and it is highly desirable to be able to recover the uranium. The foregoing process which obtains phosphoric acid at a low concentration of about 30% P.sub.2 O.sub.5 is attractive despite the added evaporation cost since uranium extraction methods currently practiced are technically and economically feasible, only when phosphoric acid concentrations are about 30% or less P.sub.2 O.sub.5.
The hemihydrate process on the other hand is desirable in that it produces phosphoric acid with a P.sub.2 O.sub.5 concentration of about 45-50% and thereby avoids the expensive evaporation step. However, disadvantageously, the hemihydrate process practiced heretofore is not suitable for uranium recovery.
It is therefore an object of the present invention to prepare high concentration phosphoric acid from phosphate rock while rendering the uranium recoverable therefrom.
It is a further object of the present invention to achieve the foregoing in an economical and commercially feasible process cycle.
Further objects and advantages of the present invention will appear hereinbelow.